codetransformer — codetransformer 0.6.0 documentation

Bytecode transformers for CPython inspired by the ast module’s NodeTransformer.

codetransformer is a library that provides utilities for working with CPython bytecode at runtime. Among other things, it provides:

• A Code type for representing and manipulating Python bytecode.
• An Instruction type, with subclasses for each opcode used by the CPython interpreter.
• A CodeTransformer type providing a pattern-based API for describing transformations on Code objects. Example transformers can be found in codetransformer.transformers.
• An experimental decompiler for determining the AST tree that would generate a code object.

The existence of codetransformer is motivated by the desire to override parts of the python language that cannot be easily hooked via more standard means. Examples of program transformations made possible using code transformers include:

• Overriding the is and not operators.
• Overloading Python’s data structure literals.
• Optimizing functions by freezing globals as constants.
• Exception handlers that match on exception instances.

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